The present invention relates to a method and an apparatus for polishing a semiconductor substrate and particularly, relates to a method and an apparatus for flattening/machining suitable for flattening/machining in the manufacturing process of the semiconductor integrated circuits.
A manufacturing process for semiconductor integrated circuits includes many processes of treatments and among them, description will be given of an interconnection process, as an example of a process to which the present invention is applicable, with reference to FIGS. 5A through 5F.
FIG. 5A shows a sectional view of a wafer on which interconnection of the first layer is formed. A dielectric film 16 is formed on a surface of a wafer substrate 15 at which a transistor section has been formed and an interconnection layer 17 made of aluminum or the like is provided on the dielectric film 16.
Since a hole is formed in the dielectric film 16 in order to ensure contact with a transistor, a portion 17xe2x80x2 of the interconnection layer 17 corresponding to the hole is more or less sunk downward. In an interconnection process for the second layer shown in FIG. 5B, a dielectric film 18 and a metal aluminum layer 19 are sequentially formed on the first layer and in addition to this, a photo-resist layer 20 for exposure is coated thereon to form an interconnection pattern of the aluminum layer.
Next, a circuit pattern, as shown in FIG. 5C, is exposed to be transferred onto the photo-resist 20 under exposure using a stepper 21. In this situation, a recess and protrusion 22 of the surface of the photo-resist layer 20 cannot be simultaneously in an in-focus condition, leading to a significant obstacle against correct photolithography due to poor optical resolution.
In order to eliminate the above described inconvenience, a flattening process for a substrate surface described below is adopted. Following the process of FIG. 5A, the dielectric layer 18, as shown in FIG. 5D, is formed and thereafter, polishing is applied on the dielectric layer 18 by the method described later such that the layer is flattened off down to the level indicated by a single dot and dash line 23 to attain a state of FIG. 5E. After the flattening, the metal aluminum layer 19 and the photo-resist layer 20 are sequentially formed on the dielectric layer 18 and the photo-resist layer 20 is then exposed with the stepper 21. In this situation, since a photo-resist surface is flat, there arises no problem due to poor optical resolution.
As a flattening process described above, there can be cited here, for example, U.S. Pat. No. 4,944,836 or Japanese laid open patent No. 59-136934 (Japanese patent publication No. 5-30052), in which a flattening/machining method using polishing is disclosed.
In FIG. 6, a diagram of a machining method generally called a chemical, mechanical polishing (CMP) method as a flattening/machining method is shown. In this FIG. 6, a polishing pad 25 is fixedly pasted on a platen 7 and the platen 7 is in rotation by a rotation driving means (a motor) 8. The polishing pad 25 is produced, for example, by slicing foam urethane resin into thin sheets and such sheets are used selecting proper characteristics and fine structure in various ways according to a kind of an object to be machined and a level of surface roughness of finish. On the other hand, a wafer 5 to be machined is fast held on a wafer holder 4 with an elastic packing pad 24 interposed between them. The wafer 5 is pushed down onto a surface of the polishing pad 25 with a load through the wafer holder 4 in rotation and further, a polishing slurry 23 is fed onto the polishing pad 25, so that protrusions of the dielectric film 18 on the surface of the wafer 5 is polished off to flatten.
In a case where a dielectric film, such as silicon dioxide and so on is polished, silica is generally used as the polishing slurry 23. Silica is a suspension obtained by dispersing high-purity fine silica particles of a particle diameter of the order 30 to 150 nm in an aqueous alkaline solution of potassium hydroxide, ammonia or the like and characterized in that a flat, smooth surface with less-work damage can be attained using it.
Further, there is provided a wafer flattening/machining technique in addition to the above described, which uses a fixed abrasive platen made of cerium oxide or the like. While a basic construction of an apparatus is similar to that of a free abrasive grain polishing technique using the polishing pad 25 shown in FIG. 6, a fixed abrasive platen 6 is mounted on a rotating platen 7 as shown in FIG. 7 instead of the polishing pad 25.
With this apparatus, machining can be carried out by feeding just water with no abrasive as a polishing liquid 23 instead of silica or the like. It should be appreciated that a flattening/machining technique in which a fixed abrasive platen 6 is used in the course of a manufacturing process of a semiconductor device has been proposed by the inventors of the present invention, for example, in a PCT patent application (International Publication Number WO 97/10613).
The fixed abrasive platen 6 is composed of abrasive grains, resins and pores. In a case where flattening/machining are carried out using such a fixed abrasive platen 6, there arises a need of a dressing process in which a surface of the fixed abrasive platen 6 is flattened with a diamond dresser, whereby active surfaces of fixed abrasive grains are exposed. If flattening/machining is carried out with no dressing process applied, local concentration of stress occurs in a surface of a wafer, resulting in adverse influences such as deterioration in uniformity across the surface of a wafer and occurrence of scratches thereon and so on.
In the case where flattening/machining is carried out using the fixed abrasive platen 6 as aforementioned in the above description of a prior art, there has been arisen a problem of instability in machining rate (fluctuations in machining amount per unit time). In order to avoid such inconveniences, dressing of the surface of the fixed abrasive platen 6 is performed prior to or during wafer machining, thereby flattening the surface thereof.
However, a performance of the fixed abrasive platen 6 though having been dressed is unstable soon after the start-up of the apparatus, thereby causing such phenomena that machining rates from wafer to wafer are varied and that uniformity across the surface of a wafer is reduced (non-uniform machining). In the prior art, in order to remove such instability, there have been inevitably required the following processes in which: the apparatus is left running with no operation done for a proper length of time after the start-up, that is, a so-called idling time is allowed for the apparatus, a dummy wafer is thereafter fed to confirm its performance and if the performance is confirmed acceptable, production gets started.
However, the requirement of the above processes results in serious problems causing increase in cost and reduction in throughput.
Consequently, it is an object of the present invention to provide a flattening/machining method using an improved fixed abrasive platen so that such a problem of the prior art technology is solved, being excellent in economics and increasing a throughput; and a flattening/machining apparatus, thereby enabling production of high reliability semiconductor devices with ease.
The inventors of the present invention have conducted experiments in various ways about a polishing method and a polishing apparatus, in which a porous fixed abrasive platen of this kind is used, in order to achieve the above described object, with the result of precious findings that in a process of wetting the fixed abrasive platen, a rapid increase in volume occurs through expansion of the fixed abrasive platen due to wetting in a given time directly after the start of wetting; a shape thereof alters so rapidly that the transformation cannot be neglected.
Therefore, the present invention was made on the basis of such findings based on the experimental facts and has a constitution in which wetting time control means properly wetting a fixed abrasive platen is provided in the body of a flattening/machining apparatus, or alternatively, wetting retaining means is provided separately from the body of the flattening/machining apparatus; with either of both means, the fixed abrasive platen is kept in a proper state of wetting in advance prior to a polishing process; and polishing can be always carried out with the fixed abrasive platen in a most optimal state of wetting at and after the start of polishing.
With such wetting retaining means, there is provided effects that a wetting control time is shortened, an operation rate of the apparatus, in turn, increases and furthermore, confirmation of performance with a dummy wafer can be omitted.
There are shown, here, typical examples of configuration of the present invention so that the above described object can be achieved:
(1) A flattening/machining method for manufacturing a semiconductor device using a porous fixed abrasive platen in which abrasive grains are fixed by a binder, the method including the step of: treating a fixed abrasive platen with wetting treatment liquid in advance prior to the use of the fixed abrasive platen in a flattening/machining process.
While wetting treatment liquid may generally be liquid whose major component is water or alcohol, or machining liquid including abrasive grains depending on circumstances, it is preferably a liquid whose major component is water in common with the machining liquid in a practical aspect. Further, a wetting treatment time in which the fixed abrasive platen is treated with the wetting treatment liquid is usually sufficient in the range from about 60 to about 100 minutes.
(2) A flattening/machining apparatus for manufacturing a semiconductor device including at least: a porous fixed abrasive platen in which abrasive grains are fixed by a binder; a rotary platen for holding the porous fixed abrasive platen; and a machining liquid supply means for supplying machining liquid onto the fixed abrasive platen,
wherein the flattening/machining apparatus further includes: a wetting time control means for performing the time control of the rotary platen for holding the porous fixed abrasive platen and the machining liquid supply means, and polishing gets started after the porous fixed abrasive platen is treated with wetting treatment liquid by the wetting time control means for a given time in advance.
Further, in the invention of (2), the following modification can also be adopted: A flattening/machining apparatus including: a wetting retaining means including at least: a treating tank in which the porous fixed abrasive platen is subjected to wetting treatment in advance; the machining liquid supply means; and a drainage means, instead of the wetting time control means, wherein not only is the wetting treatment liquid supplied to the treating tank from the machining liquid supply means of the wetting retaining means, but the porous fixed abrasive platen is subjected to the wetting treatment with the wetting treatment liquid for a given time in advance and thereafter, polishing gets started.
Accordingly, the start-up of the flattening/machining apparatus can be faster and polishing can be effective in a good condition at and after the start of polishing, thereby enabling increase in throughput.
The wetting retaining means includes not only a pressure container useful for the treating tank, but a pressurization means for introducing and pressurizing an inert gas such as nitrogen and argon, for example, in the pressure container through a valve, wherein polishing gets started after the fixed abrasive platen is subjected to a wetting treatment for a given time while being immersed in the wetting treatment liquid contained in the pressure container under a predetermined gas pressure, in advance, thereby enabling the wetting treatment time to further decrease.